In base-10, moving digits one place to the left is equivalent to multiplying by 10: 3.14, 31.4, 314. Shifting the digits one place to the right is equivalent to dividing by 10.

Base-2 works the same way: shifting bits left is equivalent to multiplication by 2: 0001 (1), 0010 (2), 0100 (4), 1000 (8). Shifting them right is equivalent to dividing by 2.

Normal binary multiplication and division are fairly logic-intensive, but multiplication and division by 2 end up producing the same results as shifting the bits left or right. Microcontroller logic units have shift circuits, so you can use those instead of the math circuits.